1. Field of the Invention
The invention is directed to a method for operating a drive unit which has an internal combustion engine and a hydraulic aggregate group such as pumps, wherein the amount of fuel supplied to the engine is controlled by a proportionally acting speed regulator. The power consumption of the hydraulic aggregate group is reduced by an electronic maximum load regulator when the engine is overloaded. When the engine is under no-load conditions, the engine speed is adjusted by an automatic idling circuit to the idling RPM and at the same time the power consumption of the aggregate group is reduced to a minimum after an arbitrary period of time. For partial-load operation, the power consumption of the aggregate group is selectively limited to a level below the maximum output of the engine.
2. Related Prior Art
A method as described above is disclosed in U.S. Pat. No. 4,763,473, issued Aug. 16, 1988. The functions, diesel overload protection, automatic idling circuit and power limitation, are monitored and regulated by a microprocessor. Adjustable hydraulic pumps are provided for the power limitation. The pumps are adjustable in accordance with power curves, in which case the choice of the power curves is made by program selection on the microprocessor and lower power ranges of the adjustable pumps can be set by proportional valves. The power limitation takes place through a hydraulic power regulator, which is expensive, while the diesel engine puts out unchanged power. The automatic idling circuit described in the aforementioned United States patent does not serve in the capacity of a power limitation of the diesel engine when a power limitation of the entire drive unit is desired.
The present invention avoids the abovementioned disadvantage and offers a method of the type in question, which operates more economically.